This invention relates to a gas absorption process and apparatus, particularly for scrubbing acetylene out of a crude gas mixture containing mostly C.sub.2 hydrocarbons.
The invention is especially directed to an improvement in the operation of a plate column, wherein the crude gas mixture is fed into the lower zone of the absorption column; fresh or regenerated absorption agent is fed to the upper zone of the absorption column; loaded absorption agent is drawn off the bottom of the absorption column and is fed to a regeneration stage; an acetylene-free product gas stream is withdrawn from the head of the absorption column, optionally after separation and recycling of a reflux condensate to the absorption column, and wherein a substantially acetylene-free liquid C.sub.2 stream is introduced into the absorption column between the respective feed points for the crude gas mixture and the absorption agent.
In the extraction of ethylene from a thermally cracked cut of hydrocarbons, a crude gas mixture is obtained containing mostly C.sub.2 hydrocarbons (ethylene, acetylene and optionally ethane). Besides the C.sub.2 hydrocarbons, the crude gas mixture may also contain C.sub.3 hydrocarbons and/or methane. Acetylene is conventionally removed from this crude gas mixture by scrubbing with an absorption agent selective for acetylene; however.
The absorption agent tends to foam under normal operating conditions, which results in downtime and/or acetylene escaping into the product gas.
The formation of both hydrocarbon-rich and hydrocarbon-poor liquid phases, in addition to the vapor phase, are generally responsible for the foam. These two liquid phases are formed when the saturation limit of the absorption agent is exceeded relative to the hydrocarbons present. But foam formation can also occur far below the saturation limit in the absorption column, particularly under unstable operating conditions.
In this connection, EP-B 158 280, corresponding to U.S. Pat. No. 4,655,798, describes a process intended to prevent foam formation by providing an additional feed of a substantially acetylene-free liquid C.sub.2 stream into the absorption column. From DE-OS 38 33 795, another process is known wherein the gaseous stream withdrawn from the head of the absorption column, is partially condensed and is recycled into the absorption column and a branched partial stream of the reflux condensate is introduced in the absorption column between the feed points for the crude gas mixture and for the absorption agent. Both of these processes, however, do not solve the problem of foam formation entirely satisfactorily.